# echo "HELLO WHO IS THIS" | tr 'A-Z' 'a-z'
# # 加密
# echo 12345 | tr '0-9' '9876543210'
# # 解密
# echo 87654 | tr '9876543210' '0-9'
# 删除字符
echo "Hello 123 world 456" | tr -d '0-9'

echo hello 1 char 2 next 4 | tr -d -c '0-9 \n'